370 THE POPULAR SCIENCE MONTHLY. 



gested in the article quoted, the mass had come from some African 

 instead of an American river, it still shows one means by which seeds 

 could be dispersed. Wallace gives further confirmation of this fact. 

 He says : " Rafts of islands are sometimes seen drifting a hundred 

 miles from the mouth of the Ganges, with living trees growing on 

 them, and the Amazon, Orinoco, Mississippi, Congo, and most great 

 rivers produce similar rafts. Spix and Martins declare that they saw 

 at different times, on the Amazon, monkeys, tiger-cats, and squirrels 

 being thus carried down the stream. . . . Admiral Smyth informed 

 Sir Charles Lyell that among the Philippine Islands after a hurricane he 

 met with floating masses of wood with trees growing upon them, so 

 that they were at first mistaken for islands, till it was found that they 

 were rapidly drifting along. . . . The fact of green trees so often 

 having been seen erect on these rafts is most important ; for they 

 would act as a sail by which the raft might be impelled in one direc- 

 tion for several days in succession, and thus at last reach a shore to 

 which a current alone could never have carried it." * Now, if such 

 rafts as these were capable of conveying large animals, it would be 

 extremely probable that they would also have on them seeds of many 

 kinds of plants ; and, as we shall see hereafter, as the animals them- 

 selves often convey unintentionally seeds sticking to their coats, they 

 too would be vehicles for their transportation. 



Besides the rafts floated down the rivers, it is very probable that 

 those which overflow their banks periodically, as the Nile, the Ganges, 

 Amazon, Orinoco, and Mississippi, or occasionally as many other riv- 

 ers do, would transport seeds from plants growing at their sources 

 to hundreds of miles below. Darwin gives the details of an experi- 

 ment he tried, which illustrates in a remarkable manner the extent to 

 which the mud of rivers and ponds is charged with seeds waiting for 

 a chance to develop. He says: " I took, in February, three tablespoon- 

 fuls of mud from three different points beneath water on the edge of a 

 little pond ; this mud when dried weighed only six and three fourths 

 ounces. I kept it covered up in my study for six months, pulling up 

 and counting each plant as it grew ; the plants were of many kinds, 

 and were altogether five hundred and thirty-seven in number ; and 

 yet the viscid mud was all contained in a breakfast-cup ! " f There 

 can be no doubt whatever that, after inundations of the land by the 

 rivers, plants spring up in localities where they were unknown before, 

 and the inference is just that the seeds were conveyed by the water. 



Birds, too, furnish another and important means of transport. 

 Many fruits having a seed incased in a hard shell are surrounded by a 

 juicy pulp : such are the cherry, plum, mistletoe-berry, hawthorn, etc. 

 All these are eaten by birds which, assimilating the pulp, cast the 

 stones in their excrement. The parasitic mistletoe has no way of 



* Wallace " Geographical Distribution of Animals," vol. i., pp. 14, 15. 

 f " Origin of Species," pp. 345, 346. 



